In order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple Input Multiple Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for next generation of communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. The IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
The IEEE 802.11 (REVmb) standard defines a Reverse Direction Grant (RDG) mechanism, which allows a station to grant time to a responding station to send data frames. The regular media access control (MAC) protocol (without RDG) may only allow transmission of an acknowledgment message after short inter-frame space (SIFS). The RDG protocol extends the regular MAC protocol to allow data transmission in addition to the acknowledgment transmission after SIFS.
As defined in the IEEE 802.11 standard, data transmissions during an RDG are restricted to frames that are addressed to the station that granted the RDG (e.g., the RDG initiator). This ‘single user’ limitation may preclude a station from sending data frames to multiple stations simultaneously, or sending data frames to the stations that are not the RDG initiator.